Suppression of Guard-Trace Resonance by Matched Termination for Reducing Common-Mode Radiation

Tetsushi WATANABE  Tohlu MATSUSHIMA  Yoshitaka TOYOTA  Osami WADA  Ryuji KOGA  

IEICE TRANSACTIONS on Communications   Vol.E93-B   No.7   pp.1746-1753
Publication Date: 2010/07/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E93.B.1746
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Advanced Electromagnetic Compatibility Technology in Conjunction with Main Topics of EMC'09/Kyoto)
Category: PCB and Circuit Design for EMI Control
printed circuit board,  common mode radiation,  guard trace,  imbalance difference model,  current division factor,  

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We propose a novel technique of matching at both ends of the guard trace to suppress resonance. This approach is derived from the viewpoint that the guard trace acts as a transmission line. We examined that matched termination suppresses guard-trace resonance through simulating a circuit and measuring radiation. We found from these results that the proposed method enables guard-trace voltages to remain low and hence avoids increases in radiation. In addition, we demonstrated that "matched termination at the far end of the guard trace" could suppress guard-trace resonance sufficiently at all frequencies. We eventually found that at least two vias at both ends of the guard trace and only one matching resistor at the far end could suppress guard-trace resonance. With respect to fewer vias, the method we propose has the advantage of reducing restrictions in the printed circuit board layout at the design stage.